1. Field of the Invention
The present invention pertains to the field of pneumatic valves. Specifically, the present invention pertains to an improved cap for use with a standard pneumatic tire valve.
2. Description of the Related Art
Valve caps for standard pneumatic tire valves have traditionally been employed to protect the valve stem from degrading due to corrosion caused by exposure to the environment. The traditional valve caps were typically manufactured from inexpensive polymer-based materials. As such, they were relatively inexpensive and weren""t aesthetically appealing. A drawback with the traditional valve cap is that they were easily removed allowing access to the valve actuating member of the valve stem so air could be released from the tire by unauthorized persons. In recent years, designer caps have come into existence.
One such cap is described in U.S. Pat. No. Des. 306,420. The designer caps are aesthetically appealing to the average person and are much more expensive than the traditional valve caps. Typically, a single designer valve cap can cost several dollars. A major drawback with the designer caps is that they are easily removed from the valve stem. Similar to the traditional valve caps, this allows unauthorized persons to release air from the tire. More significant, however, is that easy removal raises the possibility that the cap would be stolen, due to its aesthetic appeal. This is a major factor in dissuading purchasers from investing in designer caps. To reduce the probability of unauthorized removal, tamper resistant valve caps have been developed.
U.S. Pat. No. 5,630,687 and U.S. patent application Ser. No. 09/151,186 each discloses a prior art tamper resistant valve cap that includes a liner adapted for threaded engagement with a standard pneumatic tire valve stem, a sleeve rotatably mounted with the liner to shroud it and an interlocking feature to selectively prevent axial displacement between the liner and the sleeve. The interlocking feature includes a screw threaded into an aperture in the sleeve, and an annular channel on the liner, positioned to receive the screw. The annular channel has an upper surface, a lower surface and an inner surface disposed between the upper and lower surfaces. The screw is moved so that it extends into the channel resting proximate to the upper surface, but clear of both said lower and inner surfaces. In this fashion, the liner and the sleeve are in a fixed axial position with respect to each other; however, the rotatability of the sleeve with respect to the liner is maintained, preventing removal of the liner from the stem. While these valve caps provide superior protection against unauthorized removal of the same, the interlocking feature proved difficult to use and manufacture.
What is needed, therefore, is a theft resistant valve cap which has reduced complexity and facilitates removal by authorized persons while frustrating removal by unauthorized persons.
A cap for a valve includes a liner having a hollow body with first and second opposed ends that features a shoulder positioned proximate to one of the opposed ends. The liner is adapted for threaded engagement with a standard pneumatic tire valve stem. The shoulder, when employed with a sleeve rotatably mounted with the liner to shroud it, facilitates restricting removal of the cap from the valve stem to authorized individuals, only. Specifically, an interlocking mechanism extends between the liner and the sleeve and limits axial movement therebetween, while allowing rotational movement. To remove the cap from the valve stem, a key is employed which forms an interference fit with the shoulder in the liner, once the shoulder is exposed. Without the key, the sleeve merely rotates freely about the liner, thereby frustrating attempts to remove the same. In one embodiment, the shoulder is formed from a single recess located proximate one of the opposed ends having an aperture therein. Although the recess may have any shape, it is typically annular. In another embodiment, there are a plurality of recesses, pairs of which are coaxial, i.e., in opposing relation on the liner. Additionally, the shoulder may be formed by one or more protrusions extending from the liner.
The liner and sleeve may be constructed so that the sleeve covers the entire liner, excepting the portion in which the shoulder is located. In this fashion, the recess is always exposed facilitating access with the key. Alternatively, the liner and sleeve may be constructed so that the sleeve selectively covers the recess. In this manner, the liner comprises a hollow body extending along a longitudinal axis between first and second opposed ends and has an interior surface and an exterior surface, disposed opposite to the interior surface. The first end includes an aperture and the interior surface extends from the aperture, terminating proximate to the second end and includes a plurality of threads, defining a threaded chamber surrounding the longitudinal axis. The exterior surface surrounds the threaded chamber and extends between the first and second opposed ends and includes a pair of shoulders formed from a pair of recesses positioned proximate to the first end. The sleeve is positioned coaxial with the liner and completely covers the exterior surface in a first position. The exterior surface has a channel, and the sleeve includes a detent adapted to be received by channel, limiting movement between the liner and the sleeve along the longitudinal axis. The channel has a thickness, and the detent has a width. The thickness and the width are measured along a direction parallel to the longitudinal axis. The relative sizes of the width and the thickness allow sufficient movement between the sleeve and the liner to expose the pair of recesses and, therefore, the shoulders, when placed in a second position. However, the detent and the channel form an interference fit in both the first and second positions. The detent may include a reciprocating member threadably attached to the sleeve. Alternatively, the detent may include a ridge formed into the sleeve.